The technology, developed by Pacific Northwest National Laboratory (PNNL) over a 40-year period, converts waste solids from a wastewater treatment plant into biocrude and methane gas using water, heat and pressure. HTP uses subcritical water and pressure (350 °C and 207 bar) to convert the wet organics into crude oil and natural gas. The process mimics the way fossil fuels were formed—but takes 45 minutes rather than millions of years. HTP is highly efficient, capturing more than 85% of feedstock energy and using only 15% for process.

At the process conditions, water changes from a polar molecule to a non-polar molecule and becomes an extremely powerful solvent for organics. Lipids, proteins, and carbs are converted to oil. The oil and water become completely soluble until cool; sulfur and phosphorus become highly insoluble, precipitate rapidly, and are recovered as dense “ore” from the oil stage. All nitrogen is reduced to ammonia in the gas stage, recoverable by membrane or other method.

The biocrude oil, with nearly zero net new carbon emissions, will be refined in an existing refinery, while the methane gas will be sold for transport in the gas pipeline system or used at the pilot plant to offset power needs elsewhere in the plant.

If fully implemented in wastewater treatment operations across the US, the technology will produce more than two billion gallons of gasoline equivalent per year. The system also produces fertilizer byproducts.

The Central Contra Costa Sanitary District, near Oakland, California, will host the pilot system. The consortium includes the Water Environment & Reuse Foundation, which represents many of the 16,000 wastewater systems in the US. The consortium also includes Genifuel Corp. with technology from DOE’s Pacific Northwest National Laboratory, Merrick & Co., Tesoro Corp., Metro Vancouver, MicroBio Engineering, Brown and Caldwell, and more than a dozen utility partners.

SoCalGas and its partners have demonstrated that this process can very effectively convert wastewater solids into renewable natural gas, using existing infrastructure, to help replace fossil fuels and reduce greenhouse gas emissions.

This new technology could have an enormous impact on energy and waste. Converting the wastewater solids produced by treatment plants in the U.S. with hydrothermal processing could produce about 128 billion cubic feet of natural gas per year and save treatment utilities $2.2 billion in solids disposal costs. A city of one million people could produce more than 600 million cubic feet of natural gas per year, save more than $7 million per year in disposal costs, and power nearly 7,000 vehicles per day.

—Jeff Reed, SoCalGas’ director of business strategy and advanced technology